LIMESCALE REMOVING COMPOSITION

Abstract: The invention provides limescale-removing compositions of pH 1-4, comprising maleic acid, a nonionic surfactant, an anionic surfactant, a perfume and an alpha-hydroxy carboxylic acid (preferably citric acid). It is believed that the combination of alpha-hydroxy carboxylic acid with maleic acid is less toxic and less prone to decomposition than an equivalent amount of maleic acid, i.e. an amount which provides comparable limescale-removing performance. However, it is also believed that the alpha-hydroxy carboxylic acid interacts with the nonionic surfactant to destabilise the product in the absence of the anionic surfactant. Thus, there is believed to a synergistic interaction between the components which provides a stable and effective composition containing the alpha-hydroxy fatty acid as a partial replacer for the maleic acid.

Description: LIMESCALE REMOVING COMPOSITION Technical Field The present invention relates to compositions for the removal of limescale. Background to the Invention Limescale mainly comprises calcium and magnesium carbonates, and can contain lesser amounts of soap scum, protein, particulates and other soils. Limescale is formed on evaporation of water containing said soils. While the deposit formed by evaporation is initially paste-like, it hardens with time to form a recalcitrant deposit. Conventional cleaning compositions are generally buffered at alkaline pH so as to attack fatty soils. Limescale is resistant to the action of alkali and specialist cleaning compositions, of acid pH, are used to remove it. A plurality of limescale removing compositions are disclosed in EP 0253676. These compositions are thickened by means of an amine or an a ine oxide and comprise an acid which may be organic or inorganic. It is known that the use of strong acids, such as hydrochloric acid will result in prompt removal of limescale but will also result in damage to surrounding surfaces, such as bath enamels, metals and certain polymers, where these are susceptible to attack by strong acids. Limescale removing compositions of maleic acid in combination with nonionic surfactants, either in further combination with ionic detergents or with phosphoric acid are known. In the absence of nonionic surfactants cleaning efficiency is greatly reduced. Maleic acid is known to be a particularly effective limescale remover and is less prone to attack surfaces than the inorganic acids. EP 0496188 (P&G) relates to compositions with 1-15% nonionic and 4-25% of maleic acid, having a pH of 1-4. Preferred compositions are formulated at pH 1-4 and comprise maleic and nonionic at specified levels but which are substantially free of both ionic detergents and phosphoric acid. Maleic acid is produced from petrochemical sources and potentially oxidises to produce rancid odours. Maleic acid is a relatively toxic material and is moderately expensive. Other organic acids, such as citric and lactic acids are available from renewable resources, are less toxic and less prone to oxidation. However, compositions comprising citric acid together with nonionic surfactants are unstable. Brief Description of the Invention We have now determined that limescale-removing compositions of pH 1-4, comprising maleic acid, a nonionic surfactant, an anionic surfactant, a perfume and an alpha- hydroxy carboxylic acid are stable. Without wishing to be limited by any theory of operation, it is believed that the combination of alpha-hydroxy carboxylic acid with maleic acid is less toxic and less prone to decomposition than an equivalent amount of maleic acid, i.e. an amount which provides comparable limescale- removing performance. However it is also believed that the alpha-hydroxy carboxylic acid interacts with the nonionic surfactant to destabilise the product in the absence of the anionic surfactant. Thus, there is believed to be a synergistic interaction between the components which provides a stable and effective composition containing the alpha-hydroxy carboxylic acid as a partial replacer for the maleic acid. Detailed Description of the Invention It is essential that the above-mentioned compositions comprise a fragrance. The presence of a fragrance is important both to meet consumer expectations and to mask any off odours resulting from decomposition of the organic acids. In is believed that the presence of the anionic detergent is essential in order that the perfume can be solubilised in the composition. Typical levels of maleic acid in the product range from 2- 6%wt. It is preferable that the level of maleic acid is below 4%wt so as reduce toxicity and prevent the development of excessive off odours. The most preferred level of maleic acid falls into the range more than 3.0%wt and less than 4.0%wt. Preferred alpha-hydroxy carboxylic acids are lactic acid, glycolic acid and citric acid. Polycarboxylic acids, particularly citric acid is the most preferred for reasons of cost, ease of availability and weight-effectiveness. The preferred of citric acid are 2.5-10wt%, most preferably 2.5-7.5wt%. It is particularly preferably that the alpha-hydroxy carboxylic acid should be present in weight excess relative to the maleic acid. Ratio of alpha-hydroxy carboxylic acid to maleic acid is preferably in the range 1-2:1. It is preferred that the nonionic surfactants should not include any significant amounts of amine oxide. The preferred nonionic surfactants are alkoxylated alcohols. The preferred alkoxylated alcohols are selected from the group comprising ethoxylated alcohols of the general formula: R 1 -(OCH 2 CH 2 ) m -OH wherein R x is straight or branched, C 8 to C 18 alkyl or hydroxyalkyl and m is, on average, 1-14. Preferably, the alkyl chain length is C 8 -C n . It is believed that this reduces the strength of the interaction with the alpha-hydroxy carboxylic acd. The preferred average degree of ethoxylation m is 6-9 for good fatty soil detergency and high solubility in the composition. Generally, the nonionic surfactant should have a HLB in the range 12-16. The starting materials for the synthesis of these ethoxylated alcohols, are available from both natural and synthetic sources. Preferred levels of nonionic surfactant range from 0.5- 7%wt, more preferably 0.75-3%wt. Preferably the anionic surfactant comprises one or more of the group comprising: primary and secondary alcohol sulphates, alcohol alkoxy sulphates, primary and secondary alkane sulphonates and alkyl aryl sulphonates. The preferred anionic surfactants are the secondary alkane sulphonates. Most preferably the secondary alkane sulphonate is a C 12 -C 18 average chain length secondary alkane sulphonate. Preferred levels of anionic surfactant range from l-10%wt, more preferably l-6%wt. It is particularly preferred that the weight ratio between the anionic surfactant to nonionic is 3:1-1:1. It is also preferable that the alpha-hydroxy carboxylic acid is present in weight excess over the total surfactant content. The presence of a thickener is optional. Preferred thickeners, when present are xanthan gums. Preferred xanthan gums are the Kelzan (RTM) series (available from Kelco Corp) . Typical levels of xanthan gum range from 0.05-lwt%. The resulting viscosity of the composition, as measured on a Haake RV2 rotoviscometer (RTM) is preferably in the range 10-200 Pas at 20 reciprocal seconds shear and 25 Celcius, using an MV1 bob. More preferably the thickened compositions have a viscosity of 10-100 mPas under the conditions mentioned above. We have determined that thin compositions have advantages over thickened compositions in certain circumstances. In particular it is believed that products having a lower viscosity exhibit a more rapid removal of limescale. Suitable viscosities fall in the range 2-10 mPas, measured as described above, with preferred viscosities being in the range 3-7 mPas. Preferred levels of perfume range from 0.1-l%wt. Acid stable perfumes are available from a variety of sources including the Quest company. Various minor components may be present in the compositions of the present invention, these include opacifiers, colours, preservatives and fluorescers. Preferred formulations comprise: a) 2-4%wt maleic acid, b) 0.75-3%wt ethoxylated alcohol of HLB 12-16 c) l-6%wt secondary alkane sulphonate, d) 2.5-7.5%wt citric acid, and, e) 0.1-0.5%wt perfume, said compositions having a pH of 1-3 and a viscosity of 3- 7 mPas as measured on a Haake RV2 rotoviscometer (RTM) at 20 reciprocal seconds shear and 25 Celcius, using an MV1 bob. The present invention will be further described with reference to the following non-limiting examples. Examples Materials used in the examples are identified as follows maleic acid maleic acid, ex. Croda. DOBANOL 91-8 (RTM) ethoxylated alcohol, ex. Shell, SAS 30-X secondary alkane sulphonate, ex. Hoechst citric acid citric acid, ex. Biacor, perfume GC-1462, ex. Quest, dye Basacid Blue 755 (RTM) ex. BASF. Compositions were prepared by: a) preparing a main mix of maleic acid in water, followed by addition of citric acid solution, and, b) adding the SAS, DOBANOL, dye and finally perfume. Compositions were prepared as given in Table 1 below, all components being given as 100%wt. TABLE 1 maleic acid 3.5%wt DOBANOL 91-8 (RTM) 1.0%wt SAS 30-X 2.0%wt citric acid 5.0%wt perfume 0.3%wt dye 0.001%wt water to 100%wt The results given in Table 2 show the rates at which MMF5 calcite is dissolved by the composition given above (thin product) and a further example which contains a Kelzan (TM) gum thickening agent (thick product) . The thick product had as viscosity of 40 mPas whereas the thin product had a viscosity of 5 mPas. TABLE 2 Treatment Time (sec) Thin Product Thick Product (Calcite dissolved g) 20 0.30 0.10 40 0.45 0.30 60 0.60 0.50 80 0.70 0.60 120 0.75 0.65 150 0.80 0.75 180 0.85 0.80 It can be seen that products having a lower viscosity show improved performance as regards their immediate effect as compared with the product having a higher viscosity. Moreover, in comparisons between the thick and thin maleic/citric products described above and a commercially available product believed to be based simply on maleic acid, using a trained panel, it was found that users perceived that the thin product showed improvements over the two other products as regards limescale removal, ease of rinsing and odour.

Claims: CLAIMS 1. Stable, viscous, limescale-removing compositions of pH 1-4, comprising maleic acid, a nonionic surfactant, a perfume, an anionic surfactant and an alpha-hydroxy carboxylic acid. 2. Composition according to claim 1, comprising 2-4%wt maleic acid. 3. Composition according to claim 1, comprising 2.5- 10wt% alpha-hydroxy carboxylic acid. 4. Composition according to claim 1, wherein the alpha- hydroxy carboxylic acid is citric acid. 5. Composition according to claim 1 comprising 0.75-3%wt nonionic surfactant. 6. Composition according to claim 1 wherein the nonionic surfactant is an alkoxylated alcohol. 7. Composition according to claim 1 comprising 1-10% anionic surfactant. 8. Composition according to claim 1 having a viscosity of the as measured on a Haake RV2 rotoviscometer (RTM) in the range 3-7 mPas at 20 reciprocal seconds shear and 25 Celcius, using an MVl bob. 9. Composition according to claim 1 comprising: a) 2-4%wt maleic acid, b) 0.75-3%wt ethoxylated alcohol of HLB 12-16 c) l-6%wt secondary alkane sulphonate, d) 2.5-7.5%wt citric acid, and, e) 0.1-0.5%wt perfume.

Inventors: BOWDEN ELAINE ANN, FRY ALAN JOHN, BOWDEN, ELAINE, ANN, FRY, ALAN, JOHN
Applicants: BOWDEN ELAINE ANN, FRY ALAN JOHN, UNILEVER NV, UNILEVER PLC, BOWDEN, ELAINE, ANN, FRY, ALAN, JOHN, UNILEVER N.V.
Application year: 1994
Main classification: C11D3
IPC codes: C11D1, C11D3